There are image forming apparatuses having a function of enabling a used image forming apparatus to be identified from a print image. The identification of the image forming apparatus is effective in the investigation of criminal acts such that the apparatus is illegally used to forge paper money or securities. In order to identify the image forming apparatus used for print, there are image forming apparatuses that make prints by adding a particular pattern that is hardly recognized by human's eyes to an image pattern. In the image forming apparatus that makes prints by adding the particular pattern to the image pattern, up to now, although a print function of the image forming apparatus is normal, if the function of adding the particular pattern is abnormal or there occurs an abnormality caused by data of the particular pattern, print operation per se by the image forming apparatus is prohibited.
However, although the print function is normal, if the use of the image forming apparatus is prohibited because only the function of investigating a few illegal persons are abnormal, there is a risk that inconvenience is forced on a large majority of honest users.
From this viewpoint, there is desired development of the image forming apparatus that provides convenience of a user so that the image forming apparatus can be used while providing the function for investigating the illegal user, if the print function is normal even though the function for identifying the image forming apparatus used for print is abnormal.